1. Field of the invention
The present invention relates to an optical scanning module, and more particularly, to an optical scanning module with two oppositely movable lenses for changing scan resolution.
2. Description of the Prior Art
Due to advancements in computer hardware and software technology and the increasing need and demand of graphic image processing, optical scanners are rapidly gaining popularity. Of all of the many varieties of scanners, flatbed scanners are the most commonly used scanners. A flatbed scanner comprises a scanning module for scanning a document. Since a scanning module only has a single lens with only one resolution, users who need to scan documents at different resolutions need other options. Therefore, much research is being done to develop scanning modules with multiple lenses to permit more than one scanning resolution.
Please refer to FIG. 1 and FIG. 2. FIG. 1 and FIG. 2 are schematic diagrams of prior art scanning modules with two lenses. The scanning module 10 is movably installed in an optical scanner (not shown) for scanning a document 12. The scanning module 10 comprises a housing 14 with a window 16 for receiving light 18 transmitted from the document 12, an optical sensing device 20 installed within the housing 14 for converting the light 18 into image signals, and a lens module 22 installed in the housing 14 for converging the light 18 onto the optical sensing module 20. The lens module 22 comprises two parallel tracks 24, 26 installed in front of the optical sensing device 20, two plastic housings 32,34 movably installed on the two parallel tracks 24,26 respectively, two lenses 28,30 installed within the two plastic housings 32,34, respectively, for providing two different resolutions in converging the light 18 onto the optical sensing device 20, and a driving device 36 installed within the housing 14 for simultaneously driving the lenses 28, 30 in the two plastic housings 32, 34 and using one of these lenses to converge the light 18.
The scanning module 10 is equipped with two lenses 28,30 for providing the capability of scanning at more than one resolution. These two lenses are arranged in such a way as to prevent mutual interference, allowing light 18 to pass through only one of the two lenses 28,30 at a time. During operation of the scanner, however, the two plastic housings 32,34 move in the same direction simultaneously thereby necessitating wide placement of the two parallel tracks 24,26 and a large overall volume within the scanning module 10.